sichermn@beach.csulb.edu (Jeff Sicherman) (05/22/91)
I tend to prefer to get regular modems as external models for safety (to the computer system), light status visibility, easier access and portability, and upgradability of the serial port chip. However, I was wondering, given the bandwidth requirements of Fax modems, especially when receiving a fax, is there a performance or reliability penalty in choosing an external fax modem ? (Reliability in the sense of lost image.) Can the modem to computer link be bumped up higher than the fax rate (9600) to handle this ? Jeff Sicherman
hqm@ai.mit.edu (Henry Minsky) (05/22/91)
In article <1991May21.182406.25973@beach.csulb.edu>, sichermn@beach.csulb.edu (Jeff Sicherman) writes: |> |> I tend to prefer to get regular modems as external models for safety |> (to the computer system), light status visibility, easier access and |> portability, and upgradability of the serial port chip. |> |> However, I was wondering, given the bandwidth requirements of Fax |> modems, especially when receiving a fax, is there a performance or |> reliability penalty in choosing an external fax modem ? (Reliability |> in the sense of lost image.) Can the modem to computer link be bumped |> up higher than the fax rate (9600) to handle this ? |> |> Jeff Sicherman The actual speed of the fax is 9600 baud synchronous, which is faster than 9600 baud async. This means that you really do need to run the computer/fax serial line at 19200 in order not to get choked with data on reception, or have long idle periods at the ends of lines. We run 19200 to an EVEREX everfax 24/96 D (model 968-51) from a sun3. It is true that at those data rates, you might expect some noise; we haven't had a noticable problem, but apparently it was enough of a concern that the Class 2 standards committee is holding up the acceptance of the standard until they add some sort of reliable host-to-modem data-link layer to the protocol.
sl@wimsey.bc.ca (Stuart Lynne) (05/22/91)
In article <16055@life.ai.mit.edu> hqm@ai.mit.edu (Henry Minsky) writes: }In article <1991May21.182406.25973@beach.csulb.edu>, sichermn@beach.csulb.edu (Jeff Sicherman) writes: }It is true that at those data rates, you might expect some noise; we }haven't had a noticable problem, but apparently it was enough of a concern that the }Class 2 standards committee is holding up the acceptance of the standard until they }add some sort of reliable host-to-modem data-link layer to the protocol. We wouldn't want to think there might be any alterior motives to this delay ...... but unfortunately there does seem to be some behind the scenes politic'ing going on. -- Stuart Lynne Computer Signal Corporation, Canada ...!van-bc!sl 604-937-7785 604-937-7718(fax) sl@wimsey.bc.ca
tnixon@hayes.uucp (05/23/91)
In article <1991May22.043410.23038@wimsey.bc.ca>, sl@wimsey.bc.ca (Stuart Lynne) writes: > In article <16055@life.ai.mit.edu> hqm@ai.mit.edu (Henry Minsky) writes: > }In article <1991May21.182406.25973@beach.csulb.edu>, sichermn@beach.csulb.edu (Jeff Sicherman) writes: > }It is true that at those data rates, you might expect some noise; we > }haven't had a noticable problem, but apparently it was enough of a concern that the > }Class 2 standards committee is holding up the acceptance of the standard until they > }add some sort of reliable host-to-modem data-link layer to the protocol. > > We wouldn't want to think there might be any alterior motives to this delay ...... > but unfortunately there does seem to be some behind the scenes politic'ing going on. As you know, I've been an active participant in this work. I don't think there are any "alterior motives" involved, just serious and sincere technical disagreement with regard to whether or not this DTE-DCE protocol should be mandatory in all fax modems. But at the meeting of TR-29.2 earlier this month, the committee voted to make it optional. There are a few more relatively minor, but technically important, issues to be resolved (mostly having to do with handling of error conditions), and then Class 2 should be ready to go out for ballot again. I expect this to happen at the TR-29 meeting in August in Yountville, CA. -- Toby -- Toby Nixon, Principal Engineer | Voice +1-404-840-9200 Telex 151243420 Hayes Microcomputer Products Inc. | Fax +1-404-447-0178 CIS 70271,404 P.O. Box 105203 | UUCP uunet!hayes!tnixon AT&T !tnixon Atlanta, Georgia 30348 USA | Internet hayes!tnixon@uunet.uu.net